Major League Baseball’s ballpark capacities at the start of the 2021 season, as announced by teams as percentage or total of capacity, as compiled by the commissioner’s office:
| Club | Ballpark | Pct. | Starting | Capacity | Total | Capacity |
| Arizona | Chase | Field | 25% | 48,405 | ||
| Atlanta | Truist | Park | 33% | 41,184 | ||
| Baltimore | Camden | Yards | 25% | 11,000 | 45,474 | |
| Boston | Fenway | Park | 12% | 37,305 | ||
| Chicago Cubs | Wrigley | Field | 20% | 41,298 | ||
| Chicago White Sox | Guaranteed | Rate | Field | 20% | 40,126 | |
| Cincinnati | Great | American | Ball | Park | 30% | 42,319 |
| Cleveland | Progressive | Field | 30% | 34,788 | ||
| Colorado | Coors | Field | 42.6% | 21,363 | 50,480 | |
| Detroit | Comerica | Park | 20% | 8,200 | 41,083 | |
| Houston | Minute | Maid | Park | 50% | 41,168 | |
| Kansas City | Kaufmann | Stadium | 30% | 10,000 | 37,903 | |
| Los Angeles Angels | Angel | Stadium | 20% | 45,517 | ||
| Los Angeles Dodgers | Dodger | Stadium | 20% | 56,000 | ||
| Miami | Marlins | Park | 25% | 37,446 | ||
| Milwaukee | American | Family | Field | 25% | 41,700 | |
| Minnesota | Target | Field | 25.9% | 10,000 | 38,544 | |
| New York Mets | Citi | Field | 20% | 41,922 | ||
| New York Yankees | Yankee | Stadium | 20% | 46,537 | ||
| Oakland | RingCentral | Coliseum | 20% | 46,847 | ||
| Philadelphia | Citizens | Bank | Park | 20% | 8,800 | 43,651 |
| Pittsburgh | PNC | Park | 20% | 38,747 | ||
| St. Louis | Busch | Stadium | 32% | 44,383 | ||
| San Diego | Petco | Park | 20% | 40,204 | ||
| San Francisco | Oracle | Park | 20% | 41,915 | ||
| Seattle | T-Mobile | Park | 18.9% | 9,000 | 47,500 | |
| Tampa Bay | Tropicana | Field | 36% | 9,000 | 25,025 | |
| Texas | Globe | Life | Field | 100% | 40,300 | |
| x-Toronto | TD | Ballpark | 15% | 1,275 | 8,500 | |
| Washington | Nationals | Park | 12.1% | 5,000 | 41,380 |
x-playing at spring training ballpark in Dunedin, Florida